Parisa Heidari

Performance analysis of virtual machines through tracing

This paper presents extensions to the Linux trace toolkit (LTT) for efficiently tracing complete systems, from the user level to the virtual machine system level and the Xen hypervisor layer. An automated benchmark was created to measure the overhead imposed by tracing and Xen paravirtualization, comparing the performance of systems, with and without virtualization and tracing. The results show a negligible impact caused by tracing and a reasonable overhead caused by paravirtualization. For some I/O intensive applications, the overhead imposed by paravirtualization is less negligible.

Efficient Method for Checking the Existence of a Safety/ Reachability Controller for Time Petri Nets

This paper considers the Time Petri Nets (the TPN model) with controllable and uncontrollable transitions. It proposes a completely forward on-the-fly algorithm for checking the existence of a safety / reachability controller. Given a TPN and a safety / reachability property, the control consists of restricting the firing intervals of controllable transitions so that to satisfy the property of interest. Our approach, based on the TPN state class graph method, computes on-the-fly the reachable state classes of the TPN while collecting progressively subclasses to be avoided so that to satisfy the property. Three levels of control can be carried out: a static control (independent of states and markings), a marking depending control, or a state depending control. Our approach does not need to compute controllable predecessors and then split state classes as it is the case for other approaches based on exploration of state space of the system (backward and forward approaches).

QoS Assurance with Light Virtualization - A Survey

Linux containers provide a low overhead and lightweight virtualization solution that increases significantly deployment density of containers per host. Using containers, different applications are deployed as a set of micro-services. This in turn improves resource utilization and cost efficiency, system agility and continuous development, and also upgrade and runtime modification. Therefore, containers have attracted lots of attention as an alternative to virtual machines hosting the cloud applications. In spite of several advantages of containers versus virtual machines, assuring quality of the provided service is challenging. In this paper, we survey some of the available promising container orchestration solutions with particular attention to their quality of service assurance capability.

Maximally permissive controller synthesis for time Petri nets

This article proposes a fully forward on-the-fly algorithm to synthesise safety/reachability controllers for real time systems. Given a time Petri net (TPN) with controllable and uncontrollable transitions and a safety/reachability property, the control consists of limiting the firing intervals of controllable transitions to satisfy the property of interest. This algorithm, based on the state class graph method, computes on-the-fly the reachable state classes of the TPN while collecting progressively firing subintervals to be avoided so that to satisfy the property. It does not need to compute controllable predecessors and then split state classes as it is the case for other approaches based on exploration of state space of the system (backward and forward approaches). Moreover, in the category of state-dependent controllers based on the restriction of firing intervals, the algorithm, proposed here, synthesises maximally permissive controllers.

A Formal Approach for QoS Assurance in the Cloud

Cloud computing is an attractive business model offering cost-efficiency and business agility. Recently, the trend is that small and large businesses are moving their services to cloud environments. The quality of service is always negotiated between the cloud users and the cloud providers and documented in the service level agreement (SLA). Yet assuring -- or even measuring -- the quality of the provided service can be challenging. This paper proposes a formal approach for quantifying the quality of service in the cloud systems as promised in the SLA. The proposed approach uses controller synthesis to find a system configuration that meets the SLA requirement. The formal approach suggested in this paper is based on, but not limited to, %the controller synthesis of Time Petri Nets (TPN). As a case study, we focus on service availability as a key performance indicator in the SLA and for a sample set of resources providing a service, we determine the system configuration satisfying the SLA.

Controller Synthesis of Time Petri Nets Using Stopwatch

Scheduling is often a difficult task specially in complex systems. Few tools are targeted at both modeling and scheduling of the systems. In controller synthesis, a scheduler is seen as a controller to manage shared resources and timing requirements of a system. This paper proposes a time Petri net-based approach for controller synthesis and finding a scheduler using stopwatch. The solution suggested here is particularly interesting for preemptive scheduling purposes. This paper deals with time Petri nets with controllable and uncontrollable transitions and assumes that a controllable transition can be suspended and retrieved when necessary. In fact, the paper supposes that every controllable transition can be associated with stopwatch. With this hypothesis, the objective is to model a system by time Petri nets and calculate subintervals where the system violates the given property. Then, the controller associates the corresponding controllable transitions with stopwatch to suspend them in their bad subintervals. The interesting advantage of this solution is that this approach synthesizes an ordinary time Petri net model before adding stopwatch. Therefore, complicated computations and overapproximations required during controller synthesis of time Petri nets associated with stopwatch are avoided.

A Forward On-The-Fly Approach in Controller Synthesis of Time Petri Nets

P. Heidira, H. Boucheneb ?A Forward On-The-Fly Approach in Controller Synthesis of Time Petri Nets?, Petri Nets - Manufacturing and Computer Science, Pawel Pawlewski (Ed.), ISBN: 978-953-51-0700-2, InTech, August 2012,

Virtual Systems Tracing for Performance Analysis

This paper describes extensions to the Linux Trace Toolkit next generation (LTTng), to trace the Xen hypervisor for efficiently tracing complete systems. LTTng is a low impact, modular, extensible, operating system tracer, while Xen is an hypervisor based on paravirtualization. Typically, one or several instances of Linux will run on top of the Xen hypervisor. The extended LTTng is able to trace all Linux instances and the hypervisor layer to give a global view of the system. An automated benchmark was created to measure the overhead imposed by tracing and Xen paravirtualization. It compares the performance of systems, with and without virtualization and tracing. The results obtained with different tests, using this procedure, are presented and show a negligible impact caused by tracing and a reasonable overhead caused by paravirtualization. Nonetheless, for some I/O intensive applications, the overhead imposed by paravirtualization is less negligible.